h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Water is often represeted by blue colours in images, and if asked, most people say that ice is either clear or white. How come when looking at snowfields and glaciers the ice usually appears blue coloured? Is this something to do with impurities?

Water appears blue/green when in sufficient quantities due to copper oxides and similar inpurities... I see no reason why large amounts of ice wouldn't contain the same impurities.

Ice being clear is pure ice formed slowly and under pressure (I think) hence why the ice at way down in the ice caps is clear. White ice is due to the ice having lots of air bubles and impurities in it. Same reason why polar bear fur looks white when it is actually clear.

Thanks for this. This is a debate going on a few days ago after seeing a documentary. The glacial ice seemed so blue we weren't sure if it was the impurities you mentioned, or something to do with internal light refraction.

I'd heard about polar bear fur, something about them being black but the fur making them appear white due to it being clear.

Ice is actually blue. As has been said, it only looks white because of air (bubbles) in the ice.

You can see the real colour of pure ice if you look at an iceberg.

Here's some pictures : http://www.hickerphoto.com/blue-iceberg-9317-pictures.htm

The answer to the question depends entirely on how much of the substance you're talking about.

A glass of water = no color. A glass of ice = the same. It's completely transparent, reflects no light, and therefore has no color.

A large mass of water = blue. A large mass of ice = the same. Once you get enough of it together, it starts absorbing light from the red end of the spectrum, reflecting blue.

I agree. Ice is blue. Only slightly, but if you look at lumps of it about 6 foot across the effect is quite noticeable.

You can see the blue colour in this photo of quite a lot (well, 50000 tons) of pure water, without a blue sky above, taken in the Kamiokande Neutrino Detector:
http://www.aip.org/png/images/deth20.jpg

I go fishing off Lagos most weekends and ten miles or so out, the sea turns exactly this colour even with 100% cloud cover.

Water absorbs very little light but what little absorption there is is about a hundred times stronger in the red end of the spectrum than the blue so the transmitted light of both pure water and pure ice is a pale turquoise blue.

There is a very readable layman's explanation at

http://www.gi.alaska.edu/ScienceForum/ASF7/773.html

... and a more technical one at

http://www.lsbu.ac.uk/water/vibrat.html#blue

Cool picture Aurora!

Of course, it all depends on the colour of the light.